1. Field of the Invention
The present invention is directed to a printer or copier with a transfer station for simultaneous both-sided printing of a carrier material. The invention is also directed to a corotron device that can be utilized in the transfer station.
2. Description of the Related Art
High-performance printers and high-performance copiers often have the capability of printing the front side and the back side of a carrier material, for example paper. This operating mode is also called duplex printing. It is known to first print one side, for example the front side, with a toner image and to subsequently turn the carrier material over. It is then reconveyed to the same printing station in order to then print the second side, usually the back side, with a second toner image. This type of duplex printing is known both for web-shaped material as well as for a single-sheet carrier material. In such a printing mode, the overall throughput is not high due to the additional transport and the turn-over of the carrier material. Given another known solution, a printer or copier system is given two printing units, whereby each printing unit prints one side of the carrier material. In this case, considerable space for the two printer units is required within the system and the technological outlay is high.
Given a printer device disclosed by U.S. Pat. No. 5,526,107, continuous form paper is supplied to a transfer printing location of a photoconductive cylinder that has electro-photographic units at two surfaces for producing differently colored toner images. At the transfer printing location, the continuous form paper is printed with a first color on the front side; subsequently, the continuous form paper is redirected and is supplied to a printing location at the same photoconductive cylinder lying opposite the transfer printing location and the back side is printed there.
European Patent Document EP-A-0 320 985 discloses that a transfer band is employed, this carrying toner images that have been transferred from a photoconductive drum onto the transfer band. German Patent Document DE-A-197 13 964, which is identical in content with U.S. Pat. No. 5,797,077, discloses a transfer station for simultaneous printing of both sides of a carrier material (duplex printing). The transfer station contains a pivotable transfer printing station that holds a transfer band away from the carrier material in a first position, so that no toner images are transferred onto this carrier material. In this position, toner images are produced superimposed on the transfer band in order to enable a multi-color printing. In a second position, the transfer station is pivoted against the carrier material and transfers the multi-color toner image.
Published PCT application WO 87/02792 discloses a corotron device having a corotron electrode whose cooperating electrode is implemented as a metal plate. This metal plate lies at ground potential. The electrical field generated between the corotron electrode and the cooperating electrode leads to a charge influencing of the toner particles.
An object of the present invention is to create a printer or copier that enables a simultaneous printing of front side and back side of a carrier material given low outlay and with high printing quality.
This object is achieved by a printer or copier having a transfer station for the simultaneous both-sided printing of a carrier material, whereby a first endless transfer band of a first transfer module carries toner particles of a first polarity in the region of a transfer printing location, a second endless transfer band of a second transfer module carries toner particles of a second polarity in the region of the transfer printing location, the carrier material is guided at the transfer printing location between the first transfer band and the second transfer band, an electrostatic field is generated at the transfer printing location that effects that the toner particles of each and every transfer band separate from the respective transfer band as a result of electrostatic forces and adhere to the surface of the carrier material lying opposite the respective transfer band, whereby each transfer module contains a switchable transfer printing station, that, in a first operating mode (a collecting and printing mode), initially keeps the respective transfer band at a distance from the carrier material, whereas a plurality of toner images are arranged on top of one another on the respective transfer band, and the carrier material does not move forward at the transfer printing location, and then conducts the respective transfer band close to the carrier material in order to transfer the toner images arranged on top of one another there onto in common, and that, in a second operating mode (a continuous printing mode) conducts the respective transfer band close to the carrier material in order to continuously print monochromatic toner images onto the carrier printer.